The steps to get this Core project working are:

1. Create a ViewModels folder and add a ViewModel:

    public class FirstViewModel : Cirrious.MvvmCross.ViewModels.MvxViewModel
    {
         public string Hello { get { return "Hello MvvmCross"; } }
    }

2. Add an App.cs class - in it place the code to start the app with the FirstViewModel:

    public class App : Cirrious.MvvmCross.ViewModels.MvxApplication
    {
        public override void Initialize()
        {
            CreatableTypes()
                .EndingWith("Service")
                .AsInterfaces()
                .RegisterAsLazySingleton();
	
            RegisterAppStart<ViewModels.FirstViewModel>();
        }
    }
